The present invention relates to a direct-view type reflective display device that displays an image with reflected light and a prism array sheet used for the reflective display device.
Conventionally, as display devices for portable electronic equipment such as notebook personal computers (PCs), reflective display devices that display an image by reflecting external light have been commercialized. For example, a liquid crystal display device provided with a polarizing plate and a metal reflector having an uneven surface has been developed. This type of liquid crystal display device adopts a birefringence display mode where display is performed by controlling birefringence of a liquid crystal layer in an electric field, and thus only one polarizing plate is necessary.
However, the above display mode has the following problems. Light is largely absorbed by the polarizing plate, color filters, and the like. Moreover, the display is bright only when observed from the direction of the regular reflection of light incident from a light source, and thus sufficient lightness is not obtained when observed from a direction deviated from the direction of the regular reflection. Therefore, to attain good display, the observer must adjust the angle of the display device and the position at which he or she observes the display. In addition, since the direction of the regular reflection overlaps surface reflection, the display quality is low.
To solve the above problems, Japanese Laid-Open Patent Publication No. 9-288271, for example, discloses a reflective display device where the reflection surface of a reflector is tilted at a predetermined angle with respect to the display plane so that the direction of light reflected by the reflector does not overlap the direction of the regular reflection from the display plane.
As another example, SID '99 Digest, p. 954 attempts to provide bright display for the observer who observes the display from a given direction (hereinafter, the direction from which the observer views a display is referred to as the observer direction) by forming tilts on an uneven reflector.
However, the conventional reflective display devices disclosed in Japanese Laid-Open Patent Publication No. 9-288271 and SID '99 Digest, p. 954 have the following problems. In these conventional reflective display devices, the reflector needs to have a tilt face to provide both the reflection function and the off-axis function (function capable of enhancing the brightness when observed from a direction deviated from the direction of the regular reflection from the display plane). This means that a reflector having a large step must be formed immediately below an optical modulation layer, that is, a liquid crystal layer. The resultant liquid crystal layer therefore fails to have a uniform cell thickness.
The step of the reflector may be flattened after formation of the reflector. In this case, however, it is necessary to flatten the reflector with a transparent resin or the like and thereafter form a transparent electrode on the flattened surface. This complicates the fabrication process of the reflector.
FIG. 17 illustrates a conventional reflective display device 98 as described above. The reflective display device 98 includes: a liquid crystal layer 94; a retardation plate, a substrate, an alignment film, and the like (these elements are collectively denoted by the reference numeral 96) formed on the side of the liquid crystal layer 94 closer to the observer (observer side); and a reflector 91 on the side of the liquid crystal layer 94 opposite to the observer side. The reflector 91 has a plurality of tilt faces 92 on the surface thereof closer to the liquid crystal layer 94. A transparent resin 95 is formed on the tilt faces 92 to flatten the surface of the reflector 91.
In the reflective display device 98 having the above construction, in order to deviate the direction in which light outgoes from the display device 98 (indicated by arrow 99) by 30 degrees from the incident direction (indicated by arrow 93), for example, it is necessary to form the tilt faces 92 having a tilt angle of about 10 degrees on the reflector 91 as shown in FIG. 17. With such tilt faces 92 formed on the reflector 91, the distance between the liquid crystal layer 94 and the reflector 91 is large at certain positions of the tilt faces 92. At these positions, the distance between pixels (not shown) on the observer side and the reflector 91 is also large. This large distance between the pixels and the reflector 91 causes a problem of color mixture when color filters are formed on the substrate on the observer side.
In the reflective display device disclosed in Japanese Laid-Open Patent Publication No. 9-288271, where the reflector is produced separately from the display part and then placed on the outer back surface of the display part, a large gap is formed between the display part and the reflector. Due to this large gap, the parallax of the display becomes a serious problem. In addition, there are an increased amount of light rays that are incident on one pixel and outgo from another pixel. As a result, the lightness and color purity of the display decrease.
Japanese Laid-Open Patent Publication No. 8-95035 discloses a reflective display device where a prism array sheet is placed on the outer surface of a display device on the observer side to separate light for display reflected from the display device from the regular reflection of external light. However, this display device hardly provides display brightness when viewed at a position in front of the display device, at which the observer normally observes an image on the display, and substantially provides only dark display.
An object of the present invention is to provide a reflective display device capable of attaining display with high brightness for the observer present in front of the display device, and a prism array sheet used for the reflective display device.